Abstract: The leaf epidermises of the major species of Psathyrostachys, Critesion and Hordelymus in Poaceae were examined, their similarities and differences on the leaf epidermis were summarized, and the taxonomic significance of leaf epidermal features among them also were discussed. Furthermore, according to the evolutionary trends of leaf epidermal characters of the three genera, their evolutionary positions and relationships were inferred as well. The results show that the genus Psathyrostachys is the most primitive one among the three genera, the genus Critesion is slightly more advanced than the former, and the genus Hordelymus is the most advanced of them; the genus Psathyrostachys might produce immediately the genus Critesion, whereas the genus Hordelymus might derive immediately from the genus Critesion. The biosystematic relationships of the three genera are corroborated by the evolutionary trend of trispikelet in the external morphology.

Key words: Psathyrostachys, Critesion, Hordelymus, leaf epidermis, biosystematic relationship